A suspension system incorporated into a bicycle not only reduces the shock to which the rider is subjected when riding over rough terrain, but it also provides more uniform traction on rough surfaces by allowing the wheels to more closely follow the contour of the road surface. Heretofore, bicycle suspension systems have been modifications of existing motorcycle suspension designs. The incorporation of such a system in a bicycle necessarily results in a bicycle wich is unacceptably heavy for any type of competition use. In addition, during a sprint, a bicyclist will often pedal in a standing position without being seated. Such a pedaling technique subjects a bicycle to a series of downward loads which would repeatedly collapse a suspension system, causing a partial absorption of the energy input by the rider.
The instant invention was designed with bicycle moto cross ("BMX") race courses in mind. Such courses usually include level terrain as well as harsh terrain. Harsh terrain not only subjects the rider to a series of shocks, but it also restricts his speed. An effective suspension would allow higher speeds over such terrain, especially when cornering. Despite the obvious advantages of a suspension system under BMX riding conditions, the problems of weight and energy absorption must be overcome if a suspended BMX bicycle is to be competitive in a sport where maneuverability and rapid acceleration are of crucial importance.
Miyakoshi et al. in U.S. Pat. No. 4,440,413, have disclosed a variable rate suspension system for the rear wheel of motocycles which uses a system of linkages designed so that the rate of increase in the compression stroke of the shock absorber increases in proportion to the upward movement of the rear wheel relative to the main frame of the motocycle. The instant invention, on the other hand, uses a linkage system to convert arcuate motion into linear motion so that the shock absorber housing can be integral with the frame.